Lame Lothar is sent by his father to Riverrun with the response of the Twins concerning the reconciliation of House Stark with House Frey. There he relays the demands that Lord Edmure Tully is to marry a Frey and that the choice of the bride will be Lord Walder's. While in Riverrun Lothar also participates in the funeral of Hoster Tully as one of the seven nobles sending off his funeral boat, and he tells Robb that Winterfell has been burned. Lothar returns to the Twins with Robb's acquiescence to Edmure's marriage.[4]

When Robb goes to the Twins to make amends with Lord Walder Frey over breaking his marriage promise, Lothar meets him outside of the gate and behaves in a conciliatory manner. That night, he encounters Catelyn in the great hall while he is drinking with some of his relatives, behaving politely to her as well.[6] However, Lothar is one of the prime engineers of the Red Wedding massacre that is about to occur, and had planned many of the key details with Roose Bolton. It is Lothar's idea to use the song "The Rains of Castamere" as a signal for the slaughter to begin.[7] According to Merrett Frey, Lothar is more dangerous than most other members of House Frey.